When attempting to develop a printing system which is xerographically compatible, it is helpful to think of the system in terms of its parts. Thus, there is the exposure unit where the digital signal representative of the final image is converted to a light image consisting of a matrix of dots. These dots are communicated to the reproductive unit where the dots are imaged on a rotating photoconductive drum or belt. The dots on the drum create an electrostatic latent image which attracts toner to the drum corresponding to the latent image. The toner is then transferred to the print medium thereby creating on the print medium a hard copy of the original digital signal.
In common xerographic printer systems, the electrical signals are converted to light images by modulation of the light output of a laser that is in turn rastered across the drum by a rotating polygon mirror. These modulated signals are then applied to the rotating drum. In an attempt to reduce the cost and complexity of such systems and improve print quality, it is desirable to provide a system which will allow for a replacement of the laser exposure unit with a low cost, easily installable and maintainable unit.
In developing such a system, several major problems must be overcome. First of all, it is desired to make such a replacement exposure module unitary in nature and to minimize IR heating problems arising from the light source. It is also desired to construct the unit with no moving parts, a minimum of fasteners, and with no critical optical alignment problems. The unitary construction criteria gives rise to the necessity of creating a mechanism for holding and illuminating a source of light. Directing this light source properly, using low cost optics and supports, is another problem that must be overcome so as to create a very selective light path for the modulated light so that the drum does not receive extraneous images is necessary.
Thus, there is a need in the art for a unitary xerographic process exposure unit, which can maintain a stable IR, heat-free environment, while also integrating the light source socket into the unit. The optic adjustments must be such as to be easily aligned and to maintain the final image to the reproductive drum free of extraneous images.